alice starts a session on node-1
  session_start returned HTTP 200, session_id=30b58715-f06c-438b-a883-c521f21f3659
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=30b58715-f06c-438b-a883-c521f21f3659
  bob sees 2 rows tagged session_id=30b58715-f06c-438b-a883-c521f21f3659 (expected 2)